Method &amp; material for accomplishing ignition mitigation in tanks containing flammable liquid

ABSTRACT

The use of flexible foam material to provide ignition mitigation in fuel tanks is described. In one example, a system for ignition mitigation includes a number of foam blocks, wherein each foam block is pre-cut from a flexible foam material. Each foam block can have a unique profile corresponding to inner surfaces of a fuel tank at a particular sector within a compartment of the fuel tank. In other aspects, one or more of the foam blocks can include one or more upper cutouts to provide clearance for upper stiffeners in the fuel tank, one or more lower cutouts to provide clearance for lower stiffeners in the fuel tank, and one or more arcuate cutouts to provide clearance for a tank fuel pump. The foam blocks can be arranged in a stack corresponding to a sequential installation at respective sectors within the compartment of the fuel tank.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/816,150, filed on Nov. 17, 2017, which is a continuation-in-part ofU.S. patent application Ser. No. 14/851,511, filed on Sep. 11, 2015, theentire contents of which both of which applications are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION (1) Field of the Invention.

The inventive concept disclosed relates generally to methods employed toprevent and/or minimize fuel ignition, fire, and/or explosion in theinterior of tanks containing fuel or other types of flammable liquids.Different systems, materials, and methods have been used in an attemptto achieve this end, including inert gaseous material, which featuresactive systems using Halon 1301 inerting and nitrogen inerting in somemilitary aircraft. “Reactive” systems have been designed that react tothe initiation of an explosion and discharge a substance intended tosuppress the internal explosion, hopefully within milliseconds. Thesereactive systems are initiated by either physical or chemical means.

In the preferred embodiment of the instant inventive concept there aredisclosed different embodiments of specific methods of installingaccurately measured quantities of flexible foam material to fill theinternal space of tanks that hold flammable liquid, with particularemphasis on aircraft fuel tanks.

(2) Background.

Since 1959, there have been sixteen documented incidents of fuel tankignition events in aircraft. These fuel tank ignition events haveresulted in 542 fatalities, 11 hull losses and 3 incidents causingsubstantial damage. The causes of the fuel tank ignition events wereattributed as follows: 4 were caused by external wing fires, 4 byelectrostatics, 3 by faulty fuel pumps or wiring, 2 by lightning, and 3to unknown causes.

On Jul. 17, 1996, TWA Flight 800 sustained an in-flight break-up aftertaking off from Kennedy International Airport in New York, resulting in230 fatalities. The National Transportation Safety Board (“NTSB”)conducted a lengthy investigation and determined that ignition of theflammable fuel/air mixture in a center wing fuel tank had occurred,causing an explosion that disintegrated the aircraft in flight. Althoughthe exact ignition source could not be determined, the NTSB concludedthat the most likely ignition source was a short circuit outside thecenter wing fuel tank that allowed excessive voltage to enter the tankthrough electrical wiring associated with the fuel quantity indicationsystem (FQIS).

The NTSB announced their official findings regarding the TWA 800accident at a public meeting held on Aug. 22nd and 23rd, 2000 inWashington, D.C. Primarily as a consequence of TWA Flight 800, theFederal Aviation Administration (“FAA”) issued numerous airworthinessdirectives intended to reduce possible ignition sources and thereby therisk of another fuel tank explosion. On May 7, 2001, the FAA promulgatedrulemaking to establish several new transport category airplane fueltank safety requirements (66 Federal Registry 23086, May 7, 2001). Therulemaking, effective Jun. 6, 2001, included Amendment 21-78, Amendment25-102 and Special Federal Aviation Regulation (“SFAR”) No. 88 entitled“Transport Airplane Fuel Tank System Design Review, FlammabilityReduction and Maintenance Requirements.” SFAR No. 88 required that typecertificate holders and supplemental type certificate holders conduct arevalidation of the fuel tank system designs on the existing fleet oftransport category airplanes capable of carrying thirty (30) or morepassengers or a payload of 7,500 pounds or more.

Legislation was enacted as 14 CFR § 25.981 (Rule 25.981) and FAAAdvisory Circulars AC 25.981-1B and 25.981-2 were issued to providecompliance guidance. Compliance with Rule 25.981 required each applicantto develop a failure analysis for the fuel tank installation tosubstantiate that ignition sources would not be present in the fueltanks. The requirements of this section are in addition to the moregeneral propulsion failure analyses requirements of 14 CFR 25.901 and 14CFR 25.1309 that have been applied to propulsion installations.

14 CFR § 25.981 (a) (3) defines three failure scenarios that must beaddressed in order to show compliance with the rule (known as the “threephases” of compliance):

Phase A: Each single failure, regardless of the probability ofoccurrence of the failure, must not cause an ignition source;

Phase B: Each single failure, regardless of the probability ofoccurrence, in combination with any latent failure condition not shownto be at least extremely remote (i.e., not shown to be extremely remoteor extremely improbable), must not cause an ignition source; and

Phase C: All combinations of failures not shown to be extremelyimprobable must not cause an ignition source.

Compliance with 14 CFR § 25.981 (Amendment 25-125) requiresinvestigation of the airplane fuel tank system using analyticalmethodology and documentation currently used by the aviation industry todemonstrate compliance with 14 CFR 25.901 and 25.1309 but withconsideration of unique requirements included in this amendment of thisparagraph.

The Federal Aviation Administration (FAA) mandates forced certificateholders to develop and implement all design changes required todemonstrate that their aircraft meet the new ignition preventionrequirements and to develop fuel tank maintenance and inspectioninstructions. Specifically, SFAR No. 88 contains six (6) requirementsapplicable to transport category aircraft: 1) determine the highesttemperature allowed before ignition occurs; 2) demonstrate that thistemperature is not achieved anywhere on the aircraft where ignition ispossible; 3) demonstrate that ignition could not occur as a result ofany single point failure; 4) Establish Critical Design ConfigurationControl Limitations (“CDCCL”), inspections or other procedures toprevent changes to the aircraft that would result in re-introduction orcreation of ignition sources; 5) develop visible means to identifycritical features of the aircraft where maintenance, repairs oralterations would affect areas or systems of possible ignition; and 6)design of fuel tanks must contain a means to minimize development offlammable vapors in fuel tanks or a means to mitigate the effects ofignition within fuel tanks.

Maintenance of ignition source prevention features is necessary for thecontinued operational safety of an airplane's fuel tank system. One ofthe primary functions of the fuel tank system is to deliver fuel in asafe and reliable manner. Preventing ignition sources is as important afunction of the fuel system as the delivery and gauging of fuel. Thefailure of any ignition source prevention feature may not immediatelyresult in an ignition event, but a failure warrants maintenance forcontinued airworthiness because the failure could eventually have adirect adverse effect on operational safety.

There have been various solutions proposed and implemented to complywith the mandated transport category aircraft fuel tank ignitionmitigation requirements. Examples of compliance methods implementedinclude electronic solutions such as the installation of TransientSuppression Devices (“TSD”), Ground Fault Interrupters (“GFI”), andsimilar current limiting devices. These devices are deficient in thatthey retain possible failure rates that a “passive,” non-electronicsolution could resolve. Clearly, there is a need for a simplified andreliable solution to make implementation of the SFAR No. 88 compliancefeasible. A better solution would be a less expensive, passive solutionthat is applicable to commercial and private aircraft and othervehicles.

(3) Description of the Related Art, including information disclosedunder 37 CFR 1.97 and 1.98.

There are no known uses of flexible foam material in the same manner andfor purposes similar to the inventive disclosure. However at least oneentity, BAE Systems, PLC, utilizes a “tie assembly” as structuralcomponents within the interior of a liquid storage tank for the purposeof reducing hydrodynamic ram pressure and minimizing possibility ofcatastrophic failure of the fuel tank in the event of projectile impact.Ref. WO 2015/170088 A1, published Nov. 12, 2015.

BRIEF SUMMARY

The method and materials discussed in this document will focus primarilyon the use of one or more conformed, interrelated pieces of flexiblefoam material shaped to replicate the inside dimensions of an aircraftfuel tank. The inventive concept, method, and materials disclosed hereinare equally applicable to tanks designed and constructed for use invarious types of vehicles and flammable liquid storage tanks. However,for the sake of simplicity and ease of explanation, most of thediscussion will be centered on the preferred embodiment, which isconcerned with aircraft fuel tanks. The term “aircraft fuel tanks,” asused in this disclosure shall apply to integral and auxiliary fuel tanksof fixed wing aircraft, rotary wing aircraft, drones, and other types ofmachines capable of flight.

The foam material disclosed herein is intended to be used as a passivemeans to mitigate ignition in aircraft fuel tanks. The present inventiveconcept advantageously satisfies the aforementioned deficiencies inaircraft fuel tanks by providing a method of accomplishing ignitionmitigation in aircraft fuel tanks using, in the preferred embodiment,molded polyurethane safety foam in coordinated shapes to fill one tankor multiple fuel tanks.

A preferred material for this inventive concept is polyurethane safetyfoam, which is a reticulated flexible foam composed of a skeletal matrixof lightweight interconnecting strands. For purposes of this disclosure,this particular material is referred to as “Reticulated PolyurethaneFoam” (“RPF”). The RPF is also a biofuel-compatible material. There arealso other varieties of foam material currently in existence, or thatmay be developed, which will function as well as RPF, including, but notlimited to, polyether. Among these materials are polyethers, in whichthe repeating chemical unit contains a carbon-oxygen bond derivedespecially from an aldehyde or an epoxide.

Other advantages of the use of flexible foam include slosh attenuation,hydrodynamic ram attenuation, and forming a barrier against foreignobject debris. These qualities are inherent properties of many foam-typematerials, including RPF. As a surge or explosion mitigating agent, RPFattenuates the sloshing of fuel and, in some cases, eliminates the needfor structural baffles within a tank. RPF further provides for a“smooth” sine wave motion of the fuel and reduces rapid redistributionof mass.

Hydrodynamic ram effect within a fuel tank or bladder cell is causedwhen a projectile impacts the exterior structure of the fuel tank. Ramforce can be intensified when the tank is penetrated by a high explosiveincendiary (“HEI”) delayed detonating-type projectile. The matrix-typestructure of RPF absorbs a portion of the shock wave as a projectilepenetrates a fuel tank. Attenuation of hydrodynamic ram minimizes damageto the fuel tank structure by reducing the overpressure of the shockwave and helps to orient the round to prevent tumbling. The reduction offuel tank structural damage can effectively reduce fuel dischargethrough the projectile entrance and exit points.

The foreign object debris barrier capability of RPF materials is aninherent beneficial effect rather than a product specificationrequirement. The RPF used in this inventive concept is a natural filter,due to its natural structure resembling a fibrous network. The finer theporosity of a material used as a fuel filter, the greater the entrapmentof foreign objects and loose debris. The RFP material entraps loosedebris within a fuel tank and minimizes the amount of debris entering anadjacent tank, the tank fuel lines, or the engine fuel system.

Explosion within a fuel tank containing kerosene-type fuels occurs as aresult of the existence of flammable mixture in the ullage incombination with an ignition source. Examples of possible ignitionsources include incendiary ammunition penetrating the fuel tank, staticdischarges, lightning strikes, switch refueling, and electrical shorts.Reticulated polyurethane foam (RPF) is in effect a three-dimensionalfire screen, which minimizes the possibility of gasoline andkerosene-type (such as jet aircraft fuel) explosions under one or acombination of the following theories: the foam acts as a heat sink,(i.e., it removes energy from the combustion process by absorbing heat);it mechanically interferes with the compression wave that precedes theflame front in an explosion; and, the high surface-to-volume ofreticulated polyurethane foam enables the strands to collect or coalescethe droplets of fuel, thus changing the vaporous mixture in the emptyspace above the fuel level (ullage), in the tank. Coalescing causes thevaporous mixture to become lean, which minimizes possible explosion.

The present inventive concept advantageously allows for greatlyincreased effectiveness in preventing the hazardous ignition of fuelwithin aircraft fuel tanks (satisfying all three phase requirements of14 CFR § 25.981 compliance), is passive and therefore far less likely toexperience a system failure, and available at a cost of implementationfar less than that of alternative electronic solutions.

Experience in the aviation industry has shown that any fuel tank can befilled to maximum of about 85% capacity (not including a fuel swell of12%) with the internal presence of reticulated polyurethane foam, notincluding any planned voids. The foam blocks should be kept clear oftank components such as the fuel inlets, fuel sensors, valves, floatswitches, and tank vents.

Other embodiments of a foam material and method in accordance with theabove principles of the inventive concept may include alternative oroptional additional aspects. One such aspect would be use of foam ofsufficient porosity and ignition mitigation properties composed of asynthetic or naturally occurring material other than polyurethane.

Another aspect of the present invention is the use of block foammaterial in interrelated, geometrical shapes which collectively conformto the interior shapes of fuel tanks.

An important aspect of the present invention is the frequent requirementto use alternate access ports of an aircraft fuel tank to insert thefoam or foam blocks and position them in a distinct pattern to minimizeany voids along tank walls. In the case of aircraft having internal fueltanks integral to the wing, fuselage, cargo bays, or tail structure, itmay be necessary to detach certain segments of the aircraft skin toprovide access to the tank.

Another aspect of the present inventive concept is the utilization of a“fully packed” design concept. A fully packed system is defined as onewhere all potential fuel tank ullage is filled with reticulatedpolyurethane foam with cutouts for internal tank components only. Thissystem is most desirable where minimal or no tank over-pressure can betolerated.

An important objective of the present inventive concept is theutilization of a grossly “voided” design concept. A grossly voidedsystem is defined as one where the fuel tank contains strategicallypositioned reticulated foam for explosion suppression. This methodprovides for minimal weight penalty and fuel retention, and is bestsuited for a fuel system that can withstand substantial overpressures.

These and various other advantages and features of novelty whichcharacterize the inventive concept are pointed out in the accompanyingdescriptive matter and drawings which form a further part hereof. For abetter understanding of the inventive concept, its advantages, and theobjects obtained by its use, reference should be made to the drawings inwhich are illustrated and described specific examples of a method andmaterial in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a general overall fuselage-cutaway view of a Boeing®737 jet aircraft, further showing the location of the center wing fueltank.

FIG. 2 shows the location of the center wing tank of the Boeing® 737aircraft, as would be seen looking through the bottom of the fuselage,and further, a tank access panel utilized by maintenance personnel forground servicing.

FIG. 3 depicts a close-up view of the access panel to the center wingtank shown in FIG. 2.

FIG. 3(A) is an illustration of the manner in which the access panel ofFIG. 2 is removed from the exterior of the center wing tank

FIG. 4 shows a cutaway view of the structural members of the center wingtank, in accordance with section line 4-4 of FIG. 1.

FIG. 5 illustrates the profile of a specifically-shaped foam blockprecisely cut to fit the exact contour of a sector of the center wingtank.

FIG. 5(A) presents a side view of the foam block of FIG. 5.

FIG. 6 presents a stylized diagram of the aggregate of a plurality ofsequentially-arranged, pre-cut foam blocks to be installed adjacent toone another, conforming to the contour of the forward compartment of thecenter wing tank.

FIG. 7 is a stylized rendering of the center wing tank, further showingthe packing arrangement of a plurality of foam blocks properly installedin the forward compartment.

FIG. 8 depicts the first stages of installation of foam blocks on theright side of the aft compartment.

FIG. 8A shows the beginning of installation of foam blocks on the leftside of the aft compartment, the right side of the compartment havingbeen completed.

FIG. 8B depicts the start of installation of foam blocks in the middlesection of the aft compartment.

FIG. 8C depicts the completion of installation of foam blocks in the aftcompartment.

FIG. 9 is a stylized rendering of the resultant installation of all foamblocks in the forward, center, and aft compartments of the center wingtank of a typical Boeing® 737 aircraft.

FIG. 10 depicts an exploded view of exemplary foam blocks which compriseone of twelve (12) vertically-oriented columns sculpted to fit withinthe first center wing box cavity of a Boeing® 767 ER aircraft.

FIG. 11 illustrates an exploded view of the aggregate of all foam blocks(circled numbers 001-108) necessary for a complete filling of foamblocks into the first center wing box cavity of a Boeing® 767 ERaircraft.

FIG. 12 depicts the joining of the aggregate of foam blocks required tofill both wing box cavities of the 767 ER center wing tank.

DETAILED DESCRIPTION

The present inventive concept is based upon the use of preciselymeasured and contoured quantities of flexible foam material to beinserted into a tank constructed for the storage or retention of aflammable liquid. The principal intended use of this inventive conceptis for the insertion of measured quantities of flexible foam materialinto the fuel tanks of aircraft. In the typical accomplishment of thismethod, interrelated sequential groupings of blocks of flexible foammaterial are used to fill specific fuel tank(s) of an aircraft.

However, in some instances, the flexible foam material may be cut andshaped into relatively small, uniformly-sized pieces so as to fitthrough tank access ports, service bays, or other available tankopenings. The objects, features, and advantages of the concept presentedin this document are more readily understood when referring to theaccompanying drawings. The drawings, totaling seventeen (17) figures,show the basic components and functions of embodiments and/or thespecific method steps. In the several figures, like reference numbersare used in each figure to correspond to the same component as may bedepicted in other figures.

For illustrative purposes only, and not by way of limitation, themethods and systems described in this disclosure are disclosed asapplicable to Boeing® 737 or Boeing® 767 series aircraft. This detaileddescription section is merely exemplary in nature and is not intended tolimit the methods and uses shown in this inventive concept. The methoddisclosed may be utilized, with appropriate changes to the procedures,in a variety of types and locales of fuel tanks, whether on a vessel,aircraft, or affixed to the ground or a structure.

There is no intent for the applicant to be bound or constrained by anyexpressed or implied theory(ies) set forth in the relevant technicalfields, background, brief summary, or the present detailed descriptionof the inventive concept as it relates to Boeing® 737 or Boeing® 767aircraft. Further, there is no intent to confine the inventive methoddisclosed to one particular make, model, or series of aircraft, orparticular configurations of aircraft fuel tanks.

The flexible foam material referred to in this document may be comprisedof any of a variety of different foam materials, including differentstructures, textures, chemical compositions, and constituent qualities.A preferred foam material is reticulated polyurethane. Additionally, anymaterial selected from the group consisting of polyethers in which therepeating unit contains a carbon-oxygen bond derived especially from analdehyde or an epoxide may be used in the method set forth in thisinventive concept.

By way of illustration only, and not as a limitation, the preferredembodiment of the present inventive concept depicts the use ofcontoured, interrelated, sequential groupings of foam blocks to fill aspecific fuel tank or tanks of an aircraft. In situations where a fueltank is relatively small, comprises an irregular shape, or its locationmakes it difficult to access, flexible foam pieces of certain shapes andsizes may be inserted through ports, openable panels, or other means,until the tank is determined to be fully satiated with the foam pieces.

When utilizing specifically-cut foam blocks, the blocks are engineered,fabricated, and/or sculpted to occupy a volumetric sector, or sectors,of the interior of a fuel tank. By utilizing the disclosed methods ofinstalling blocks 50 or foam pieces to fill one or more fuel tanks of anaircraft, the aircraft operator prevents or minimizes the potentiallydamaging or catastrophic effects of fuel ignition, fire, and/orexplosion.

For ease of explanation and illustrative purposes only, and not as ameans of limitation, the disclosed method is described with regard toinstallation of the foam blocks into the center wing tank 112 of aBoeing® 737 aircraft 110 or the center wing box cavities 211, 212, of aBoeing® 767 aircraft 200.

The discussion of the present inventive concept will be initiated withFIG. 1, which illustrates an overall view of a Boeing® 737 jet aircraft110. FIG. 1 also depicts the fuselage 111, and a center wing tank 112,which is encircled. As in most similar jet aircraft, the predominance ofthe fuel load is generally carried in fuel tanks constructed within theleft wing 104 and right wing 105, with equal quantities in each wing104, 105. The wing-loaded fuel serves to add a counter-balancing weightto offset the upward wing structural bend due to the aerodynamic liftforce generated by the wings 104, 105 when in flight. However, forsubstantially increased range, the aircraft 110 may be loaded withadditional fuel in the center wing tank 112 and other internal tanks, ifavailable.

FIG. 2 is a stylized rendering looking upward at the undersurface of theBoeing® 737 fuselage 111, further revealing the location of the centerwing tank 112. Also shown in FIG. 2 is a center wing tank access panel20 utilized by maintenance personnel during ground servicing of thisparticular model and series of the Boeing® 737.

FIG. 3 depicts an expanded view of the access panel 20 shown in FIG. 2.FIG. 3(A) is an illustration of the manner in which the access panel 20is removed from the exterior of the center wing tank 112, furthershowing a clamp ring 21, one of a plurality of washers 22, and one of aplurality of bolts 23, the washers 22 and bolts 23 utilized forinsertion through apertures 24 for fastening the clamp ring 21 onto alower center wing panel 26.

FIG. 4 illustrates a stand-alone sectional view of the center wing tank112, in accordance with section line 4-4 of FIG. 1. The structuralintegrity of the center wing tank 112, as positioned within the fuselage111, substantially determines the internal contour of the center wingtank 112. The internal wing tank 112 contour, on initial determinationof the quantity of foam material required, can be divided into aplurality of volumetric sectors, each sector amenable to acceptance ofone, a few, or a substantial quantity of foam blocks or piecesconforming to each sector.

Referring to FIG. 4, the aircraft 110 structural members shown include afront spar 120, rear spar 121, floor beams 122, and a tank ceiling 127abutting the aircraft floor beams 122. It is important to note that, asshown in FIG. 4, the center wing tank 112 comprises multiplecompartments: a forward compartment 131, a center compartment 132, andan aft compartment 133. The three compartments 131, 132, 133 areseparated by spanwise beam #2 124 and spanwise beam #1 125. In each ofthe three compartments 131, 132, 133, a fuel tank floor 128 compriseslower stiffeners 128 and the fuel tank ceiling 127 comprises upperstiffeners 129, which give additional rigidity to all three tankcompartments 131, 132, and 133.

As a planning consideration, it is important to assess the structuralarrangement and means of access to each individual compartment of a tankwith multiple compartments. This is vital in order to arrive atpre-determined working order as to which of the compartments should bethe first to be filled with the foam material and in what sequence theremaining compartments should be filled.

As further discussion of the installation of aggregate foam blocks 50,explanation will be given of the methodology and process of measuring,sizing, and sculpting an exemplary foam block 50. Shown in FIG. 5 thereis illustrated, by way of example, a profile view of a forwardcompartment foam block 51. This forward compartment foam block 51 isdesignated as such due to the fact that the contour of its outerperimeter corresponds to the shape, internal fittings and components ofa specific, sector within the forward compartment 131 of the center wingtank 112.

In viewing FIG. 5, the topmost edge shows four upper cutouts 52 whichprovide clearance for upper stiffeners 129 of the forward compartment131 as previously shown in FIG. 4. The left edge 55 of the foam block 51is fabricated so as to correspond to the forward tank wall 123, andfurther shows an arcuate cutout 53 which provides clearance for a tankfuel pump, or other tank component. The bottommost section of theforward compartment foam block 51 illustrates three cutouts 54 whichallow clearance for the three lower stiffeners 130 of the forwardcompartment 131, as shown in FIG. 4. Thus, the sector into which thisfoam block is placed manifests upper stiffeners 129, lower stiffeners130, the forward tank wall 123, and a portion of a fuel pump.

The right edge 56 of the forward compartment foam block 51 correspondsto spanwise beam #2 124, as is depicted in FIG. 4. FIG. 5(A) is a viewlooking directly at the right edge 56 of the forward compartment foamblock 51, and further showing the nominal width 57 of the forwardcompartment foam block 51. The dimensions of each of the foam blocks 50have been measured and fabricated or sculpted in a size and contourwhich is completely dependent upon the size and contour of the fuel tanksector into which the specific foam block is to be installed.

As observed in FIG. 5, a directional UP arrow and a forward (FWD) arroware printed on the surface of the foam block 51 to further guide aninstaller or technician in placing this particular foam block 51 in thecorrect orientation. Aircraft mechanics will also need foam blockorientation and positioning guidance in the event one or more foamblocks 50 may need to be removed for internal tank or tank componentinspection or maintenance during aircraft line operations.

The illustrated forward compartment foam block 51 of FIG. 5 is furthergiven a part number (P/N) to indicate its exact location in the forwardcompartment 131 of the center wing tank 112. The part number alsodefines the order of its loading in the installation sequence of theaggregate of all foam blocks 50. The general manner of construction ofthe contour of the previously-described forward compartment foam block51 is typical of the parameters to be met for each of the aggregate foamblocks 50 to be inserted in the forward compartment 131 of the centerwing tank 112 of a Boeing® 737 series 400 aircraft as well as those foamblocks to be installed in the mid compartment and aft compartment of thecenter wing tank 112. Similarly, the general manner of construction ofthe contour of any other foam block described above is typical of theparameters to be met for any foam block to be installed in any of avariety of aircraft fuel tanks.

The contours of the aggregate of all foam blocks 50 are a culmination ofdeterminations made of the dimensions, profile, connections,attachments, and integral components of the inner surfaces of the fueltank at the specifically designated sectors internal to each theforward, center, and aft compartments 131, 132, 133 of the center wingtank 112. This methodology is applicable to the determination of thesize and contour of any foam block that may be fabricated for insertioninto any of an unlimited variety of fuel tanks.

In planning a project for installation of foam blocks in the center wingtank 112, the initial process requires the manufacture and delivery of apre-determined quantity of bulk foam material. The bulk forms generallymeasure approximately 12′×4′×2′. However, in everyday applicability, theoverall dimensions and volumetric quantity of the bulk material isdependent upon the size and contour of the particular type of fuel tankinto which the finished sculpted foam pieces are to be inserted.

During the manufacturing process, the bulk quantities of flexible foammay be colored, as required by the customer. In the preferredembodiment, a purple color facilitates the trouble-shooting of fuelcontamination or irregularities associated with fuel lines, the enginefuel pump, filters, etc. Purple-colored flexible foam enables adetermination whether an ignition event or possible foam deteriorationhas taken place.

By way of example only, in the case of the center wing tank 112 of a-300 series Boeing® 737 aircraft, engineering drawings are executed in asequential series of scaled renderings of volumetric sectors of, forinstance, the forward compartment 131 of the center wing tank 112. Theprofile of the compartment is measured and scaled at regularly-spacedincrements along a line extending from a selected wall, tank floor, orthe ceiling of the forward compartment 131. The measurements also takeinto consideration the placement of tank structural components andequipment. In the same manner, engineering drawings are rendered for theinterrelated sectors and contour of the center compartment 132 and aftcompartment 133 of the center wing tank 112.

A plurality of cutouts of foam blocks 50 is made from the manufacturedbulk foam, each block cut and sculpted according to thepreviously-described scaled renderings and further, each block cutout isprogressively identified with a part number (P/N). Further, orientatingsymbols or text, such as “UP,” “DOWN,” “REAR,” or “FORWARD,” may beprinted thereon. Cutting and shaping of the individual foam blockcutouts from the bulk material may be accomplished by use of severaloptional means. These options include, but are not limited to mechanicalblade type-cutting, specially designated/manufactured smooth blade typecutting tools, an extremely fine-toothed band saw-type blade, or ahot-wire type cutting tool.

Once the entirety of the aggregate foam blocks 50 required for thecenter wing tank 112 have been sculpted, each block is identified with apart number (P/N) and numerical or alphabetical sequencing correspondingto the sequential placement of the foam block into its correspondingsector within each of the forward, center, or aft compartments 131, 132,133. The foam blocks 50 are individually packaged and arranged in astack or stacks which correspond to the orderly, sequential installationof the foam blocks 50 into the appropriate sector previously calculated.Further, detailed written instructions regarding the installation of thefoam in each compartment are drafted and organized in a manual for theguidance of technicians who will install the foam blocks 50.

To install the foam blocks 50 into the center wing tank 112, it ispreferable to position the aircraft 110 on a level surface and at aconvenient height for access to the center wing tank 112. The accessopening cover is then removed and the foam blocks 50 are insertedthrough the access openings with the exercise of care to avoid tearingor abrading the foam blocks on the lip of the opening. FIG. 2, FIG. 3and FIG. 3(A) illustrate the relative position of the access panel 20 ofthe center wing tank 112.

In many instances, installation of the foam blocks may be accomplishedduring the manufacturing or initial assembly stages of a fuel tank. Inthese situations, the job of the technicians or installers is much lessproblematic, since access to the interior of the tank is relativelystraightforward and convenient. As a preliminary step, in installationof the flexible foam into fuel tanks that have been in service for aperiod of time, the cleanliness of the tank must first be ensured bydraining the tank, purging, and then vacuuming the interior.

As stated previously, a very specific order of insertion of the foamblocks 50 must be followed so that all spaces that are intended to befilled in the center wing tank 112 are indeed filled. Empty spaces inthe tank can only be those left by design, which is referred to as“planned voiding.” The center wing tank 112 under discussion here shouldbe filled with the foam blocks 50 fitted according to the sectors andpattern specified in the previously-mentioned engineering drawings andinstallation instructions.

By way of further illustration, FIG. 6 depicts a diagram of arepresentative sample of a plurality of sequentially-arranged, pre-cutfoam blocks 50 to be installed adjacent to one another, therebyconforming to the interior contour of the forward compartment 131 of thecenter wing tank 112 of the Boeing® 737 aircraft. Each of the blocks 50has a shape and an order of installation which ultimately conforms to aspecific contour of the forward compartment 131 at a particular sectorof the forward compartment 131. FIG. 7 is a stylized “see-through”rendering of the center wing tank 112, further showing the packingarrangement of a plurality of blocks 50 in the process of beinginstalled in the forward compartment 131 of the center wing tank 112.

Generally, the installation of the foam blocks 50 is accomplished bytechnicians entering through existing fuel tank access bays andopenings. Further, a certain amount of the foam blocks 50 may beuploaded directly into the tank 112. On aircraft other than the Boeing®737, existing fuel tank access openings that may be used for insertionand installation include, but are not limited to, maintenance accessholes, wet and dry access bays found on non-cylindrical auxiliary fueltanks, inspection holes in belly tanks, and the like. In the case of anaircraft having integral wing tanks, for instance, access may benecessary by means of removing a portion of the wing skin to access thefuel tank.

A very specific order of insertion of the foam blocks 50 must befollowed so that all spaces that are intended to be filled in the tankare indeed filled. The method disclosed in this document must take intoconsideration the fact that all tanks designed to contain flammableliquid, including aircraft fuel tanks, manifest distinctive shapes andcontours of the tank floor, ceiling, and walls.

Care is necessarily exercised to avoid tearing or abrading the foam onthe lip of the access bays or holes. Shaped block foam pieces areinserted and positioned in a manner to ensure that the required internaltank void is filled and maximum ignition source prevention is achieved.The foam material selected for this disclosed method is considered to be“memory foam.” Memory foam generally returns to its original shape aftercompression down to 40% of its original volume. A key feature of thepresent inventive concept is that the design and structure of the shapedblock foam pieces allows them to be bent or slightly compressed in orderto fit through existing access bays or ports of various aircraft fueltanks.

In referring to FIGS. 8, 8A, 8B and 8C, it is to be noted that themajority of Boeing® 737 series 300 and series 400 aircraft arecharacterized by a first internal access port 18 between the aftcompartment 133 and the center compartment 132 of the aircraft and asecond internal access port 19 between the center compartment 132 andthe forward compartment 131. Further, a lower access panel 20 isdepicted at the midpoint of the forward compartment 131, which coincideswith the underside of the fuselage.

In the installation of foam blocks 50 into the center wing tank 112 of aBoeing® 737 aircraft, the procedure begins with the right side of theaft compartment 133 of the center wing tank 112. The installer(s) mustgain access to the aft compartment 133 first, through a lower accesspanel 20 located on the underside of the fuselage 111 of the aircraft,as shown in FIG. 2 and FIG. 3. Access is sequentially accomplishedthrough the second internal access port 19, and the first internalaccess port 18.

FIG. 8 depicts a quantity of foam blocks 50 having been installed on theright side of the aft compartment 133. Next, the installer(s) work theleft side of the aft compartment 133, FIG. 8A showing the completion ofinstallation of foam blocks on the left side of the aft compartment 133,the right side of the compartment 133 having been completed. As theinstaller(s) begins exiting the aft compartment 133 through the firstaccess port 18, he/she installs RPF blocks 50 in the middle section ofthe aft compartment 133, as shown in FIG. 8B. FIG. 8C depicts thecompletion of installation of foam blocks 50 in the aft compartment 133.

FIG. 9 illustrates a stylized diagram of the resultant installation ofall foam blocks in the forward, mid, and aft compartments 131, 132, 133of the center wing tank 112 of a typical Boeing® 737 aircraft.

For illustrative purposes, renderings of the method of foam filling ofthe center wing tank 210 of a Boeing® 767 ER aircraft 200 is shown inFIG. 10, FIG. 11, and FIG. 12. For informational purposes, the specificmodel 767 ER illustrated is constructed with a center wing tank 210consisting of a first center wing box cavity 211 and a second wing boxcavity 212.

Beginning with FIG. 10, there is shown an exploded view of a column often foam blocks 64-73 which comprise one of twelve (12)vertically-oriented columns designed to fill contiguous sectors of thefirst center wing box cavity 211 of the Boeing 767® ER aircraft 200.Each block 64-73 manifests cutouts and a shape to fit the first centerwing box cavity 211 contour and/or structural components correspondingto the sector into which the blocks 64-73 are sculpted to fit. FIG. 11depicts an exploded view of the aggregate of all foam blocks (circlednumbers 001-108) which are necessary to comprise a complete filling offoam material into the first center wing box cavity 211.

In turning to FIG. 12, there is shown a stylized rendering of thejoining of the assemblies of foam blocks required to fill both the firstcenter wing box cavity 211 and the second center wing box cavity 212 ofthe Boeing® 767 ER 200. The foam blocks depicted as filling the secondcenter wing box cavity 212 are structured and arranged similarly to therequired assembly of foam blocks for the first center wing box cavity211. As a result, the union of these two groups of foam blockscompletely fills the center wing tank 210 of the 767 ER aircraft 200with ignition mitigating foam.

When conducting any of the above described methods and procedures, thefitted size, shape and installation of any aggregate of flexible foammaterial should be such that no internal tank voids longer than 2.5 feetexist (with the internal tank fuel probes installed). All flexible foamblocks must be kept clear of the tank components such as the fuel ports,fuel probes, float switches, and tank vents. The “planned” voiding areasaround these structures should not exceed a volume of 10% of the totalfuel tank volume and there should be no additional connecting voidsbetween any of the planned void spaces. The minimum space of foam filledarea required between the planned void areas is three (3.0) inches ifmaximum void size is used.

While the present invention has been described above in terms ofspecific embodiments, it is understood that the invention is not limitedto these disclosed embodiments. It is not intended to be exhaustive orto limit the invention to the precise form disclosed. Manymodifications, variations, and other embodiments of the invention willcome to mind of those skilled in the art to which this inventionpertains, and which are intended to be and are covered by both thisdisclosure and hereafter submitted claims. It is indeed intended thatthe scope of the invention should be determined by proper interpretationand construction of the hereafter submitted claims and their legalequivalents, as understood by those of skill in the art relying upon thedisclosure in this specification and the attached drawings. It isintended that the scope of the invention is not limited to anyparticular aircraft, or to any particular type of tank constructed tohold flammable liquid.

What is claimed is:
 1. A system for ignition mitigation, comprising: afirst plurality of foam blocks, individual foam blocks among the firstplurality of foam blocks being pre-cut to conform in shape with acontour of a first compartment of a fuel tank at a particular sectorwithin the first compartment of the fuel tank; and a second plurality offoam blocks, individual foam blocks among the second plurality of foamblocks being pre-cut to conform in shape with a contour of a secondcompartment of the fuel tank at a particular sector within the secondcompartment of the fuel tank.
 2. The system of claim 1, wherein eachfoam block among the first plurality of foam blocks has a unique profilecorresponding to inner surfaces of the fuel tank at a specificallydesignated sector within at least one compartment of the fuel tank. 3.The system of claim 1, further comprising: a third plurality of foamblocks, individual foam blocks among the third plurality of foam blocksbeing pre-cut to conform in shape with a contour of a third compartmentof the fuel tank at a particular sector within the third compartment ofthe fuel tank.
 4. The system of claim 3, wherein the first compartmentcomprises a forward compartment of the fuel tank, the second compartmentcomprises a center compartment of the fuel tank, and the thirdcompartment comprises an aft compartment of the fuel tank.
 5. The systemof claim 1, wherein the fuel tank comprises at least one of a centerwing tank or an auxiliary fuel tank.
 6. The system of claim 1, whereinat least one foam block among the first plurality of foam blockscomprises at least one upper cutout to provide clearance for upperstiffeners in the fuel tank.
 7. The system of claim 1, wherein at leastone foam block among the first plurality of foam blocks comprises atleast one lower cutout to provide clearance for lower stiffeners in thefuel tank.
 8. The system of claim 1, wherein at least one foam blockamong the first plurality of foam blocks comprises at least one arcuatecutout to provide clearance for a tank fuel pump.
 9. The system of claim1, wherein the first plurality of foam blocks are arranged in a stackcorresponding to a sequential installation at respective sectors withinat least one compartment of the fuel tank.
 10. The system of claim 1,wherein at least one foam block among the first plurality of foam blockscomprises a directional indicator to indicate an installationorientation at a sector within at least one compartment of the fueltank.
 11. The system of claim 1, wherein at least one foam block amongthe first plurality of foam blocks comprises an identifier to indicatean installation location at a sector within at least one compartment ofthe fuel tank.
 12. The system of claim 11, wherein the identifierfurther indicates a relative order of installation of the at least onefoam block, in sequence, among the first plurality of foam blocks withinthe at least one compartment of the fuel tank.
 13. The system of claim1, wherein at least one foam block among the first plurality of foamblocks comprises a specified color.
 14. The system of claim 1, whereinthe first plurality of foam blocks are formed from a flexible foammaterial.
 15. The system of claim 14, wherein the flexible foam materialcomprises reticulated polyurethane foam.
 16. The system of claim 14,wherein the flexible foam material comprises polyether foam.
 17. Asystem for ignition mitigation, comprising: a plurality of foam blocks,wherein: each foam block among the plurality of foam blocks is pre-cutfrom a flexible foam material; and each foam block among the pluralityof foam blocks has a unique profile corresponding to inner surfaces of afuel tank at a particular sector within a compartment of the fuel tank.18. The system of claim 17, further comprising: a second plurality offoam blocks, wherein each foam block among the second plurality of foamblocks has a unique profile corresponding to inner surfaces of the fueltank at a particular sector within a second compartment of the fueltank.
 19. The system of claim 17, wherein the compartment comprises atleast one of a forward compartment of the fuel tank, a centercompartment of the fuel tank, and an aft compartment of the fuel tank.20. The system of claim 17, wherein the fuel tank comprises at least oneof a center wing tank or an auxiliary tank.
 21. The system of claim 17,wherein at least one foam block among the plurality of foam blockscomprises at least one upper cutout to provide clearance for upperstiffeners in the fuel tank.
 22. The system of claim 17, wherein atleast one foam block among the plurality of foam blocks comprises atleast one lower cutout to provide clearance for lower stiffeners in thefuel tank.
 23. The system of claim 17, wherein at least one foam blockamong the plurality of foam blocks comprises at least one arcuate cutoutto provide clearance for a tank fuel pump.
 24. The system of claim 17,wherein the plurality of foam blocks are arranged in a stackcorresponding to a sequential installation at respective sectors withinthe compartment of the fuel tank.
 25. The system of claim 17, wherein atleast one foam block among the plurality of foam blocks comprises adirectional indicator to indicate an installation orientation at asector within the compartment of the fuel tank.
 26. The system of claim17, wherein at least one foam block among the plurality of foam blockscomprises an identifier to indicate an installation location at a sectorwithin the compartment of the fuel tank.
 27. The system of claim 26,wherein the identifier further indicates a relative order ofinstallation of the at least one foam block, in sequence, among theplurality of foam blocks within the compartment of the fuel tank. 28.The system of claim 17, wherein the plurality of foam blocks are formedfrom a flexible foam material.
 29. The system of claim 28, wherein theflexible foam material comprises reticulated polyurethane foam.
 30. Thesystem of claim 28, wherein the flexible foam material comprisespolyether foam.